View Compilation Error

0_0_30367072_29150.cpp: In function 'int main()':
0_0_30367072_29150.cpp:32:56: error: 'gcd' was not declared in this scope
                 printf("%lld/%lld\n",a[i]/gcd(a[i],b[i]),b[i]/gcd(a[i],b[i]));
                                                        ^